140 THE BLOOD. 



Urea and the Urates. In 1823 Provost and Dumas 1 

 discovered urea in the blood of animals from which the 

 kidneys had been removed ; which was the first experimental 

 demonstration that this principle is formed in the system and 

 eliminated by, not manufactured in, the kidneys. It was 

 demonstrated in healthy blood by Marchand, 2 in 1838, and 

 since then has been recognized as one of its normal constit- 

 uents, though existing in very minute quantity. These 

 observations have been confirmed by numerous French, Ger- 

 man, and English physiologists. The urate of soda also exists 

 in small quantity in the blood, and possibly the hippurate of 

 soda. The reason why the proportion of these principles is 

 so small, is that they are eliminated by the proper organs as 

 soon as formed. 



Cholesterine. This substance was demonstrated in the 

 blood by Denis in 1830. 3 It is now known to exist in this 

 fluid in considerable quantity. It is most abundant in the 

 blood coming from the nervous centres, where it is produced 

 in great part, and is diminished in the passage of the blood 

 through the liver. 4 



A substance was described by Boudet in 1833, in the 

 blood, which he called Seroline. Its existence in the blood 

 is problematical. 6 



Creatine and Creatinine. Yerdeil and Marcet have de- 

 monstrated the presence of these substances in the blood.' 

 Their proportion is very small, and has not been determined. 

 They undoubtedly have the same relation to the system as 

 urea and cholesterine. 



1 Annales de Chimie et de Physique, 1821, tome xviii., p. 280. 



2 Annales des Sciences Naturelles, 1838, 2me serie, tome x., p. 46. 



3 ROBIN and VERDEIL, op. cit., tome ii., page 63. 



4 See an article by the author on a New Excretory Function of the Liver, 

 American Journal of the Medical Sciences, October, 1862. 



6 Ibid. 



6 ROBIN and YERDEIL, Chimie Anatomique, tome ii., pp. 480 and 489 



